Transmit-and-receive module and communication device

ABSTRACT

A transmit-and-receive module includes a duplexer, a power amplifier, and a low-noise amplifier. The duplexer includes a transmit filter and a receive filter. The power amplifier and the low-noise amplifier are integrated with each other. In a Smith chart, impedance in a receive band of the receive filter seen from a receive terminal intersects a line connecting a center point of noise figure circles and a center point of gain circles. The center point of the noise figure circles represents the impedance at which the noise figure of the low-noise amplifier is minimized. The center point of the gain circles represents the impedance at which the gain of the low-noise amplifier is maximized.

This application claims priority from Japanese Patent Application No.2016-155017 filed on Aug. 5, 2016. The content of this application isincorporated herein by reference in its entirety.

BACKGROUND

The present disclosure relates to a transmit-and-receive moduleincluding a low-noise amplifier and a power amplifier and to acommunication device including the transmit-and-receive module.

In accordance with a decreased size of a front-end module mounted on amobile terminal, a transmit front-end unit, and a receive front-end unitare being integrated with each other (being formed into a module) by wayof the integration of radio-frequency components.

Japanese Unexamined Patent Application Publication No. 2001-53544discloses an antenna-integrated amplifier module including a duplexerfor separating radio-frequency signals from each other according to thefrequency, a low-noise amplifier, and a power amplifier (see FIG. 14 ofthis publication).

BRIEF SUMMARY

In the above-described antenna-integrated amplifier module, impedancematching is performed so that input/output impedance of the duplexer,input impedance of the low-noise amplifier, and output impedance of thepower amplifier can match the characteristic impedance (about 50Ω, forexample).

In the above-described antenna-integrated amplifier module, however, themere adjustment between the input impedance of the low-noise amplifierand the output impedance of the receive side of the duplexer by usingthe characteristic impedance fails to optimize the noise figure (NF) ofthe low-noise amplifier.

To address the above-described problem, the present disclosure providesa transmit-and-receive module which is small in size and which candecrease the noise figure while a duplexer, a power amplifier, and alow-noise amplifier are integrated with each other, and provides acommunication device including the transmit-and-receive module.

According to an embodiment of the present disclosure, there is provideda transmit-and-receive module including a duplexer, a power amplifier,and a low-noise amplifier. The duplexer includes a common terminal, atransmit terminal, a receive terminal, a transmit filter unit, and areceive filter unit. A radio-frequency transmit signal and aradio-frequency received signal are input into and output from thecommon terminal. A radio-frequency transmit signal is input into thetransmit terminal. A radio-frequency received signal is output from thereceive terminal. The transmit filter unit uses a transmit band as apass band and is connected to the common terminal and the transmitterminal. The receive filter unit uses a receive band as a pass band andis connected to the common terminal and the receive terminal. The poweramplifier amplifies a radio-frequency transmit signal and outputs theamplified radio-frequency transmit signal to the transmit terminal. Thelow-noise amplifier amplifies a radio-frequency received signal inputand received from the common terminal via the duplexer and the receiveterminal. The power amplifier and the low-noise amplifier are integratedwith each other. In a Smith chart, impedance in the receive band of thereceive filter unit seen from the receive terminal intersects a lineconnecting a center point of noise figure (NF) circles and a centerpoint of gain circles. The center point of the NF circles represents theimpedance at which a noise figure of the low-noise amplifier isminimized. The center point of the gain circles represents the impedanceat which gain of the low-noise amplifier is maximized.

In the related art, a low-noise amplifier handling low-power signals anda power amplifier handling high-power signals are formed in differentmodules. In this configuration, impedance matching between the low-noiseamplifier and a duplexer is performed by using the characteristicimpedance of a front-end circuit. In this case, the output impedance ofa receive filter unit is set so as to maximize the gain of the low-noiseamplifier. In contrast, in the above-described configuration accordingto an embodiment of the disclosure, the low-noise amplifier and thepower amplifier are integrated with each other in the same module. Toperform impedance matching between the low-noise amplifier and theduplexer, instead of using the characteristic impedance, the outputimpedance of the receive filter unit is set so as to optimize both ofthe gain and the noise figure of the low-noise amplifier. It is thuspossible to provide a transmit-and-receive module which is small in sizeand which achieves the optimized balance of the receiving noise figureand the receiving gain while a power amplifier, a duplexer, and alow-noise amplifier are integrated with each other.

The receive filter unit may have output impedance which intersects theline connecting the center point of the NF circles and the center pointof the gain circles in the Smith chart. The transmit filter unit mayhave input impedance at which gain of the power amplifier is maximized.

With this configuration, the input impedance of the transmit filter unitis set so as to achieve the optimized balance of the gain and theefficiency of the power amplifier, while the output impedance of thereceive filter unit is set to be a value different from thecharacteristic impedance so that both of the gain and the noise figureof the low-noise amplifier can be optimized. This eliminates the need toprovide an impedance matching circuit between the receive filter unitand the low-noise amplifier to perform impedance matching therebetweenby using the characteristic impedance. It is thus possible to provide atransmit-and-receive module which is small in size and which achievesthe optimized balance of the receiving noise figure and the receivinggain while a power amplifier, a duplexer, and a low-noise amplifier areintegrated with each other.

A value of receive impedance used for impedance adjustment between thereceive filter unit and the low-noise amplifier may be different from avalue of transmit impedance used for impedance matching between thetransmit filter unit and the power amplifier.

Impedance matching between the power amplifier and the duplexer isperformed by using the characteristic impedance of the front-end circuitso that the balance of the gain and the efficiency of the poweramplifier can be optimized. In contrast, customized impedance deviatingfrom the characteristic impedance is used for impedance adjustmentbetween the low-noise amplifier and the duplexer so that both of thegain and the noise figure of the low-noise amplifier can be optimized.Accordingly, the value of the receive impedance and that of the transmitimpedance are different from each other. It is thus possible to enhanceisolation characteristics in a path from the input terminal (moduletransmit terminal) of the power amplifier to the output terminal (modulereceive terminal) of the low-noise amplifier via the duplexer.

The value of the receive impedance used for impedance adjustment betweenthe receive filter unit and the low-noise amplifier may be higher thanthe value of the transmit impedance used for impedance matching betweenthe transmit filter unit and the power amplifier.

With this configuration, the output impedance of the receive filter unitis higher than the input impedance of the transmit filter unit. It isthus possible to enhance isolation characteristics in a path from theinput terminal of the power amplifier to the output terminal of thelow-noise amplifier via the duplexer.

The value of the receive impedance may be higher than the value of thetransmit impedance by a factor of about 1.4 or greater.

The present inventors have found that, when the receive impedance ishigher than the transmit impedance by a factor of about 1.4 or greater,it is possible to enhance the isolation while decreasing the receivingnoise figure, compared with when the receive impedance is equal to thetransmit impedance. That is, when the center point of NF circles of thelow-noise amplifier is located on the higher impedance side than thecenter point of gain circles is, by setting the impedance in the receiveband of the receive filter unit to be higher than the input impedance ofthe transmit filter unit by a factor of about 1.4 or greater, thereceiving noise figure can be decreased substantially withoutnecessarily decreasing the receiving gain. Additionally, as thedifference between the output impedance of the receive filter unit andthe input impedance of the transmit filter unit (characteristicimpedance, for example) is greater, the isolation can be improved to ahigher level.

The value of the receive impedance may be higher than the value of thetransmit impedance by a factor smaller than about 2.3.

The present inventors have found that it is possible to enhance theisolation while decreasing the noise figure when the receive impedanceis higher than the transmit impedance by a factor smaller than about2.3, compared with when the receive impedance is equal to the transmitimpedance. The present inventors have also found that, when the centerpoint of NF circles of the low-noise amplifier is located on the higherimpedance side than that of gain circles is, if the output impedance inthe receive band of the receive filter unit is set to be higher than theinput impedance in the transmit band of the transmit filter unit by afactor of about 2.3 or greater, the gain of the low-noise amplifier issignificantly decreased and the noise figure thereof is also increased.When the receive impedance is higher than the transmit impedance by afactor smaller than about 2.3, the receiving noise figure can bedecreased substantially without necessarily decreasing the receivinggain.

The transmit-and-receive module may further include a second duplexer, asecond power amplifier, and a second low-noise amplifier. The secondduplexer includes a second common terminal, a second transmit terminal,a second receive terminal, a second transmit filter unit, and a secondreceive filter unit. A radio-frequency transmit signal and aradio-frequency received signal are input into and output from thesecond common terminal. A radio-frequency transmit signal is input intothe second transmit terminal. A radio-frequency received signal isoutput from the second receive terminal. The second transmit filter unituses a second transmit band different from the transmit band as a passband and is connected to the second common terminal and the secondtransmit terminal. The second receive filter unit uses a second receiveband different from the receive band as a pass band and is connected tothe second common terminal and the second receive terminal. The secondpower amplifier amplifies a radio-frequency transmit signal and outputsthe amplified radio-frequency transmit signal to the second transmitterminal. The second low-noise amplifier amplifies a radio-frequencyreceived signal input and received from the second common terminal viathe second duplexer and the second receive terminal.

With the above-described configuration, in a multiband-support front-endcircuit, impedance matching between the duplexers and the low-noiseamplifiers disposed in plural signal paths connected to the antenna isperformed as follows. In each signal path, instead of using thecharacteristic impedance, customized impedance reflecting the amplifyingcharacteristics and the noise figure characteristics of the low-noiseamplifier is used for impedance matching between the duplexer and thelow-noise amplifier. It is thus possible to provide atransmit-and-receive module which is small in size and which achievesthe optimized balance between the receiving noise figure and thereceiving gain according to the frequency band while plural poweramplifiers, plural duplexers, and plural low-noise amplifiers supportingmultiple bands are integrated with each other.

According to another embodiment of the present disclosure, there isprovided a communication device including the above-describedtransmit-and-receive module and a radio-frequency signal processingcircuit. The radio-frequency signal processing circuit processes aradio-frequency received signal input from the transmit-and-receivemodule and processes a radio-frequency transmit signal and outputs theprocessed radio-frequency transmit signal to the transmit-and-receivemodule.

It is thus possible to provide a transmit-and-receive module which issmall in size and which achieves the optimized balance of the receivingnoise figure and the receiving gain while a power amplifier, a duplexer,and a low-noise amplifier are integrated with each other.

According to an embodiment of the present disclosure, it is possible todecrease the size and the noise figure of a transmit-and-receive moduleand a communication device in which a duplexer, a power amplifier, and alow-noise amplifier are integrated with each other.

Other features, elements, characteristics and advantages of the presentdisclosure will become more apparent from the following detaileddescription of embodiments of the present disclosure with reference tothe attached drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a circuit diagram of a transmit-and-receive module accordingto a first embodiment;

FIG. 2 is a circuit diagram of a transmit-and-receive module accordingto a comparative example;

FIG. 3A illustrates customized impedance matching for a receive filterin the first embodiment;

FIG. 3B illustrates characteristic impedance (about 50Ω) matching for areceive filter in the comparative example;

FIG. 4 illustrates the impedance of receive filters intransmit-and-receive modules according to first through third examplesand a comparative example;

FIG. 5A is a Smith chart illustrating the relationship of the in-bandimpedance of the receive filter to NF circles and gain circles in thefirst example;

FIG. 5B is a Smith chart illustrating the relationship of the in-bandimpedance of the receive filter to NF circles and gain circles in thecomparative example;

FIG. 6 is a graph illustrating comparison results of the noise figure ofthe transmit-and-receive module of the first example and that of thecomparative example;

FIG. 7A is a graph illustrating comparison results of isolationcharacteristics of a single duplexer of the first example and those ofthe comparative example;

FIG. 7B is a graph illustrating comparison results of receive-bandtransmission characteristics of a single duplexer of the first exampleand those of the comparative example;

FIG. 8A is a Smith chart illustrating the relationship of the impedanceof the receive filter to NF circles and gain circles in the firstexample;

FIG. 8B is a Smith chart illustrating the relationship of the impedanceof the receive filter to NF circles and gain circles in the secondexample;

FIG. 8C is a Smith chart illustrating the relationship of the impedanceof the receive filter to NF circles and gain circles in the comparativeexample;

FIG. 9A is a graph illustrating comparison results of the isolationbetween power amplifiers and low-noise amplifiers according to the firstexample, the second example, and the comparative example;

FIG. 9B is a graph illustrating comparison results of receive-bandtransmission characteristics between duplexers and the low-noiseamplifiers according to the first example, the second example, and thecomparative example;

FIG. 10A is a Smith chart illustrating the relationship of the impedanceof the receive filter to NF circles and gain circles in the thirdexample;

FIG. 10B is a graph illustrating comparison results of receive-bandtransmission characteristics between the duplexers and the low-noiseamplifiers according to the third example and the comparative example;and

FIG. 11 is a circuit diagram of a communication device and atransmit-and-receive module according to a second embodiment.

DETAILED DESCRIPTION

Transmit-and-receive modules and a communication device according toembodiments of the present disclosure will be described below in detailthrough illustration of examples with reference to the drawings. All ofthe embodiments described below illustrate general or specific examples.Numeric values, configurations, materials, components, and positions andconnection states of the components illustrated in the followingembodiments are only examples, and are not described for limiting thepresent disclosure. Among the components illustrated in the followingembodiments, the components that are not recited in the independentclaims will be described as optional components. The sizes anddimensional ratios of the components in the drawings are not necessarilyillustrated as actual sizes and ratios.

First Embodiment 1.1 Circuit Configuration of Transmit-and-ReceiveModule

FIG. 1 is a circuit diagram of a transmit-and-receive module 1 accordingto a first embodiment. The transmit-and-receive module 1 includes aduplexer 10, a power amplifier (PA) 20, a low-noise amplifier (LNA) 30,a matching circuit 21, an adjusting circuit 31, a module common terminal110, a module transmit terminal 120, and a module receive terminal 130.

The duplexer 10 includes a common terminal 101, a transmit terminal 102,a receive terminal 103, a transmit filter 10T, and a receive filter 10R.With this configuration, the duplexer 10 is able to simultaneously passa radio-frequency (RF) transmit signal in a transmit band from thetransmit terminal 102 to the common terminal 101 and a RF receivedsignal in a receive band from the common terminal 101 to the receiveterminal 103 by using the frequency-division duplexing (FDD) method.

The common terminal 101 is connected to the module common terminal 110.The duplexer 10 transmits a RF transmit signal and receives a RFreceived signal through the common terminal 101. The transmit terminal102 is a terminal into which a RF transmit signal is input via themodule transmit terminal 120, the power amplifier 20, and the matchingcircuit 21. The receive terminal 103 is a terminal from which a RFreceived signal is output via the module common terminal 110, the commonterminal 101, and the receive filter 10R.

The transmit filter 10T is a transmit filter unit using a transmit bandas a pass band and being connected to the common terminal 101 and thetransmit terminal 102. The receive filter 10R is a receive filter unitusing a receive band as a pass band and being connected to the commonterminal 101 and the receive terminal 103.

The power amplifier 20 is a power amplifier circuit that amplifies a RFtransmit signal input from the module transmit terminal 120 and outputsthe amplified RF transmit signal to the transmit terminal 102 via thematching circuit 21.

The low-noise amplifier 30 is a low-noise amplifier circuit thatamplifies a RF received signal input from the module common terminal 110via the receive filter 10R and the adjusting circuit 31.

The matching circuit 21 is a circuit for providing impedance matchingbetween the power amplifier 20 and the transmit filter 10T. The matchingcircuit 21 provides impedance matching so that the impedance of thepower amplifier 20 seen from the transmit terminal 102 can match thecharacteristic impedance (about 50Ω, for example).

The adjusting circuit 31 is a circuit for adjusting the input impedanceof the low-noise amplifier 30. The adjusting circuit 31 adjusts theimpedance of the low-noise amplifier 30 seen from the receive terminal103 to the characteristic impedance (about 50Ω, for example).

In the transmit-and-receive module 1 according to the first embodiment,the provision of the matching circuit 21 and the adjusting circuit 31may be omitted.

The module common terminal 110 is an external connecting terminal thatcan be connected to a communication medium, such as an antenna. Themodule transmit terminal 120 is an external connecting terminal forconnecting the power amplifier 20 and a RF signal processing circuit (RFintegrated circuit (RFIC)) (not shown) disposed subsequent to the poweramplifier 20. The module receive terminal 130 is an external connectingterminal for connecting the low-noise amplifier 30 and the RFIC (notshown).

To reduce the size of the transmit-and-receive module 1, the poweramplifier 20 handling high-power signals and the low-noise amplifier 30handling low-power signals are integrated with each other. In the firstembodiment, integrating of the power amplifier 20 and the low-noiseamplifier 30 with each other is not restricted to forming of the poweramplifier 20 and the low-noise amplifier 30 into one chip. An amplifierelement forming the power amplifier 20 and an amplifier element formingthe low-noise amplifier 30 may be made separately and formed in the samepackage or be mounted on the same mounting substrate. Such aconfiguration is also included in integrating of the power amplifier 20and the low-noise amplifier 30 with each other.

1.2 Circuit Configuration of Transmit-and-Receive Module according toComparative Example

In some transmit-and-receive modules of the related art, a transmitmodule handling high-power signals and a receive module handlinglow-power signals are not integrated with each other.

FIG. 2 is a circuit diagram of a transmit-and-receive module accordingto a comparative example. As shown in FIG. 2, this transmit-and-receivemodule is constituted by a transmit module 500 and a receive module 600.That is, unlike the transmit-and-receive module 1 according to the firstembodiment, in the transmit-and-receive module of the comparativeexample, the transmit module 500 and the receive module 600 are formedas different chips and are not integrated with each other. Thetransmit-and-receive module of the comparative example is also differentfrom the transmit-and-receive module 1 in the mode of impedance matchingbetween a receive filter 510R and the receive module 600.

1.3 Comparison of Impedance Matching between First Embodiment andComparative Example

FIG. 3A illustrates customized impedance matching for the receive filter10R in the first embodiment. FIG. 3B illustrates characteristicimpedance (about 50Ω) matching for the receive filter 510R in thecomparative example.

In the transmit-and-receive module shown in FIG. 2 in which the transmitmodule 500 handling high-power signals and the receive module 600handling low-power signals are separately formed, impedance matchingbetween a low-noise amplifier 530 and the receive filter 510R of aduplexer 510 is performed by using the characteristic impedance (about50Ω, for example) of a front-end circuit. In the transmit-and-receivemodule of the comparative example, as shown in FIG. 3B, to maximize thegain of the low-noise amplifier 530, a matching circuit 531 adjusts theimpedance of the low-noise amplifier 530 so that the center point ofgain circles (equal gain circles) of the low-noise amplifier 530 can bethe characteristic impedance (about 50Ω). To maximize the gain of thelow-noise amplifier 530, the output impedance of the receive filter 510Ris set so that it can coincide with the center point (characteristicimpedance) of the gain circles, as shown in FIG. 3B.

In contrast, in the transmit-and-receive module 1 of the firstembodiment, the low-noise amplifier 30 and the power amplifier 20 areintegrated with each other. Instead of performing impedance matchingbetween the low-noise amplifier 30 and receive filter 10R by using thecharacteristic impedance (about 50Ω) of the front-end circuit, theimpedance of the receive filter 10R is set so as to increase the gain ofthe low-noise amplifier 30 and to decrease the noise figure (NF)thereof. That is, in the transmit-and-receive module 1 of the firstembodiment, instead of maximizing the gain of the low-noise amplifier30, the impedance of the receive filter 10R is set so as to optimizeboth of the gain and the noise figure of the low-noise amplifier 30.More specifically, in the Smith chart shown in FIG. 3A, the outputimpedance of the receive filter 10R is set so that the impedance in thereceive band of the receive filter 10R seen from the receive terminal103 can intersect a line connecting the center point of the NF circlesand that of the gain circles.

The impedance, the NF circles, and the gain circles in the receive pathof the first embodiment and those of the comparative example are basedon the direction in which the receive filter is seen from the low-noiseamplifier, as indicated in the lower sections of FIGS. 3A and 3B. The NFcircle (equal NF circle) represents the output impedance of the receivefilter at which the noise figure of the low-noise amplifier 30 includingthe adjusting circuit 31 is equal. The gain circle (equal gain circle)represents the output impedance of the receive filter at which the gainof the low-noise amplifier 30 including the adjusting circuit 31 isequal. The center point of the NF circles represents the outputimpedance in the receive band of the receive filter at which the noisefigure of the low-noise amplifier 30 including the adjusting circuit 31is minimized. The center point of the gain circles represents the outputimpedance in the receive band of the receive filter at which the gain ofthe low-noise amplifier 30 including the adjusting circuit 31 ismaximized.

With the configuration of the transmit-and-receive module 1 of the firstembodiment, it is possible to provide a transmit-and-receive modulewhich is small in size and which achieves the optimized balance of thereceiving noise figure and the receiving gain while a power amplifier, aduplexer, and a low-noise amplifier are integrated with each other.

1.4 Characteristics Comparison of Transmit-and-Receive Modules accordingto Examples and Comparative Example

FIG. 4 illustrates the impedance of receive filters intransmit-and-receive modules according to first through third examplesand a comparative example. FIG. 4 shows that the impedance of thelow-noise amplifier seen from the receive terminal 103 is Z1 (Ω), theimpedance of the receive filter seen from the receive terminal 103 is Z2(Ω), and the impedance of the other elements (the impedance of the poweramplifier seen from the transmit terminal 102 and the impedance of theantenna seen from the common terminal 101) is all about 50Ω.

The table on the right side in FIG. 4 shows that Z2 of atransmit-and-receive module of a first example is about 80Ω, that of asecond example is about 70Ω, and that of a third example is about 110Ω.Z1 of the transmit-and-receive modules of the first through thirdexamples and that of the comparative example are all about 50Ω.

FIG. 5A is a Smith chart illustrating the relationship of the in-bandoutput impedance of the receive filter 10R to NF circles and gaincircles in the first example. FIG. 5B is a Smith chart illustrating therelationship of the in-band output impedance of the receive filter to NFcircles and gain circles in the comparative example.

Concerning the transmit-and-receive module of the comparative example inwhich the transmit module 500 and the receive module 600 are separatelydisposed, the Smith chart in FIG. 5B shows that the impedance in thereceive band of the receive filter 510R seen from the receive terminal103 (duplexer Rx in-band impedance in FIG. 5B) does not intersect a line(L1 in FIG. 5B) connecting the center point (NF in FIG. 5B) of the NFcircles and that (Ga in FIG. 5B) of the gain circles. The impedance inthe receive band of the receive filter 510R is located at the center(characteristic impedance) of the Smith chart.

In contrast, concerning the transmit-and-receive module 1 of the firstexample, the Smith chart in FIG. 5A shows that the impedance in thereceive band of the receive filter 10R seen from the receive terminal103 (duplexer Rx in-band impedance in FIG. 5A) intersects a line (L1 inFIG. 5A) connecting the center point (NF in FIG. 5A) of the NF circlesand that (Ga in FIG. 5A) of the gain circles. As a result, the impedanceof the receive filter 10R of the first example is separated farther fromthe center (characteristic impedance) of the Smith chart and is shiftedtoward the higher impedance side, and is thus located closer to thecenter point of the NF circles than that of the receive filter 510R ofthe comparative example is.

FIG. 6 is a graph illustrating comparison results of the noise figure ofthe transmit-and-receive module 1 of the first example and that of thecomparative example. More specifically, this graph illustratescomparison results of the noise figure in the receive band between themodule common terminal 110 and the module receive terminal 130 of thefirst example and that of the comparative example. As a result ofshifting the output impedance of the receive filter 10R of thetransmit-and-receive module 1 of the first example toward the centerpoint of the NF circles, as shown in FIG. 5A, the noise figure isdecreased in the entire receive band by about 0 to 0.4 dB compared withthat of the transmit-and-receive module of the comparative example.

With the above-described configuration of the transmit-and-receivemodule 1 of the first example, it is possible to decrease the receivingnoise figure while the power amplifier 20, the duplexer 10, and thelow-noise amplifier 30 are integrated with each other.

To form a small transmit-and-receive module by integrating a poweramplifier and a low-noise amplifier with each other, the performance ofcircuit elements such as an inductor and a capacitor used for anadjusting circuit 31 is sacrificed. This may reduce the Q factor of theadjusting circuit 31, which may lead to an increase in the receivingnoise figure of the transmit-and-receive module. However, in thetransmit-and-receive module 1 of the first embodiment, instead ofmaximizing the gain of the low-noise amplifier 30, impedance adjustmentis performed so as to achieve the optimized balance of the noise figureand the gain. This makes it possible to reduce the size of thetransmit-and-receive module 1 without necessarily sacrificing thereceiving performance even with a decrease in the Q factor of theadjusting circuit 31.

The transmit-and-receive isolation characteristics and the transmissioncharacteristics in the receive path of the transmit-and-receive moduleswill now be described below.

FIG. 7A is a graph illustrating comparison results of the isolationcharacteristics of a single duplexer of the first example and those ofthe comparative example. More specifically, this graph illustratesisolation characteristics of a single duplexer between the transmitterminal 102 and the receive terminal 103 of the first example and thoseof the comparative example. FIG. 7A shows that the isolationcharacteristics of the transmit-and-receive module 1 of the firstexample are improved particularly in the transmit band, compared withthe comparative example.

In the transmit-and-receive module 1 of the first example, the receiveimpedance used for impedance adjustment between the receive filter 10Rand the low-noise amplifier 30 is about 80Ω. The receive impedance usedfor impedance adjustment between the receive filter 10R and thelow-noise amplifier 30 is the output impedance in the receive band ofthe receive filter 10R to optimize the balance between the noise figureand the gain of the low-noise amplifier 30. The transmit impedance usedfor impedance matching between the transmit filter 10T and the poweramplifier 20 is set so that the input impedance of the transmit filter10T can achieve the optimized gain and efficiency of the power amplifier20, and more specifically, the input impedance of the transmit filter10T is set to be about 50Ω. The transmit impedance used for impedancematching between the transmit filter 10T and the power amplifier 20 is,for example, the input impedance in the transmit band of the transmitfilter 10T for causing the transmit impedance to match the impedance ofthe matching circuit 21.

That is, in the transmit-and-receive module 1 of the first example, thevalue of the receive impedance and that of the transmit impedance aredifferent. More particularly, in the first example, the value of thereceive impedance is higher than that of the transmit impedance. Theisolation characteristics are thus improved, as shown in FIG. 7A,because of the difference in the impedance between the transmit path andthe receive path in the signal path from the transmit terminal 102 tothe receive terminal 103.

FIG. 7B is a graph illustrating comparison results of receive-bandtransmission characteristics of a single duplexer of the first exampleand those of the comparative example. More specifically, this graphillustrates transmission characteristics of a single duplexer (receivefilter) between the common terminal 101 and the receive terminal 103 ofthe first example and those of the comparative example. FIG. 7B showsthat the insertion loss in the receive band of the transmit-and-receivemodule 1 of the first example is increased, compared with thecomparative example. The reason for this is that the receive impedancein the first example deviates from the characteristic impedance which isabout 50Ω, and this makes the in-band transmission characteristicsappear to be decreased. However, the transmission characteristics in thepath between the module common terminal 110 and the module receiveterminal 130 including the low-noise amplifier 30, the adjusting circuit31, and the duplexer 10 are maintained, which will be discussed later indetail with reference to FIG. 9B.

The relationship between the above-described receive impedance and theisolation characteristics will be described below.

FIG. 8A is a Smith chart illustrating the relationship of the outputimpedance of the receive filter 10R to NF circles and gain circles inthe first example. FIG. 8B is a Smith chart illustrating therelationship of the output impedance of the receive filter 10R to NFcircles and gain circles in the second example. FIG. 8C is a Smith chartillustrating the relationship of the output impedance of the receivefilter 510R to NF circles and gain circles in the comparative example.

FIG. 8A illustrates out-of-band impedance characteristics of the receivefilter 10R in addition to the impedance characteristics of thetransmit-and-receive module 1 (Z2=about 80Ω) according to the firstexample shown in FIG. 5A. FIG. 8B illustrates the impedancecharacteristics of the receive filter 10R of the transmit-and-receivemodule 1 (Z2=about 70Ω) according to the second example. FIG. 8Cillustrates out-of-band impedance characteristics of the receive filter510R in addition to the impedance characteristics of thetransmit-and-receive module (Z2=about 50Ω) according to the comparativeexample shown in FIG. 5B.

As shown in FIGS. 8A through 8C, as the receive impedance Z2 increasessuch as about 50Ω (comparative example), about 70Ω (second example), andabout 80Ω (first example), the receive-band output impedance of thereceive filter approaches closer to the center point (NF) of the NFcircles from the center point (Ga) of the gain circles. Additionally,the transmit-band impedance (Tx1-Tx2 in FIGS. 8A through 8C) of thereceive filter varies in accordance with a change in the receiveimpedance Z2. More specifically, impedance Z₀ of the receive filter 10Rof the first example corresponding to Tx2 (862 MHz) is Z₀(0.114+j1.400)(=70.2Ω). Impedance Z₀ of the receive filter 10R of the second examplecorresponding to Tx2 (862 MHz) is Z₀(0.098+j1.196) (=60.0Ω). ImpedanceZ₀ of the receive filter 510R of the comparative example correspondingto Tx2 (862 MHz) is Z₀(0.096+j1.146) (=57.5Ω). This shows that, as thereceive impedance Z2 increases, the output impedance in the transmitband of the receive filter separates farther from the characteristicimpedance (about 50 Ω) and farther from the center point (Ga) of thegain circles. That is, as the impedance of the receive filter 10R isshifted toward the higher impedance side, the transmit-band impedancecan separate farther from the center point of the gain circles. Thisreduces the gain in the transmit band of the receive filter 10R, therebymaking it possible to enhance the transmit-and-receive isolationcharacteristics.

FIG. 9A is a graph illustrating comparison results of the isolationbetween the power amplifiers and the low-noise amplifiers according tothe first example, the second example, and the comparative example. Thisgraph illustrates the isolation characteristics (PA-LSA isolation)between the module transmit terminal 120 and the module receive terminal130. FIG. 9A shows that the isolation, particularly in the transmit-bandisolation, of the transmit-and-receive module 1 of each of the first andsecond examples is improved, compared with the transmit-and-receivemodule of the comparative example. The isolation of thetransmit-and-receive module 1 in the first example is improved to ahigher level than that of the second example. This validates that thetransmit-and-receive isolation characteristics are improved to a higherlevel as the difference between the receive impedance (output impedanceof the receive filter 10R) used for impedance adjustment between thereceive filter 10R and the low-noise amplifier 30 and the transmitimpedance (input impedance of the transmit filter 10T) used forimpedance matching between the transmit filter 10T and the poweramplifier 20 is greater.

FIG. 9B is a graph illustrating comparison results of the receive-bandtransmission characteristics between the duplexers and the low-noiseamplifiers according to the first example, the second example, and thecomparative example. This graph illustrates the transmissioncharacteristics (DupRx-LNA transmission characteristics) between themodule common terminal 110 and the module receive terminal 130. FIG. 9Bshows that, even with a difference between the receive impedance and thetransmit impedance, the transmission characteristics in the receive pathdo not deteriorate, but are maintained, compared with the comparativeexample in which the receive impedance and the transmit impedance matchthe characteristic impedance (about 50Ω).

That is, as shown in FIGS. 8A through 8C, by reducing the gain of thetransmit band in the receive path as a result of separating thetransmit-band impedance of the receive filter 10R farther from the gaincircles, the transmit-and-receive isolation characteristics can beimproved while maintaining the transmission characteristics of thereceive band.

The above-described comparison results of the first and second examplesand the comparative example show that, when the transmit impedance isabout 50Ω, the receive impedance can be 70Ω) or higher. That is, thereceive impedance can be higher than the transmit impedance by a factorof about 1.4 or greater.

The present inventors have found that, when the receive impedance ishigher than the transmit impedance by a factor of about 1.4 or greater,as in the second example, it is possible to enhance the isolation whiledecreasing the receiving noise figure, compared with when the receiveimpedance is equal to the transmit impedance. That is, when the centerpoint of NF circles of the low-noise amplifier is located on the higherimpedance side than the center point of gain circles is, by setting theimpedance in the receive band of the receive filter 10R to be higherthan the input impedance of the transmit filter 10T by a factor of about1.4 or greater, the receiving noise figure can be decreasedsubstantially without necessarily decreasing the receiving gain.Additionally, as the difference between the output impedance of thereceive filter 10R and the input impedance of the transmit filter 10T(characteristic impedance, for example) is greater, the isolation can beimproved to a higher level.

FIG. 10A is a Smith chart illustrating the relationship of the outputimpedance of the receive filter 10R to NF circles and gain circles inthe third example.

FIG. 10A illustrates the impedance characteristics of the receive filter10R of the transmit-and-receive module 1 (Z2=about 110Ω) according tothe third example. As shown in FIG. 10A, when the receive impedance Z2is about 110 the receive-band impedance (Rx1 to Rx2 in FIG. 10A) of thereceive filter 10R approaches even closer to the center point (NF) ofthe NF circles from the center point (Ga) of the gain circles than thatof the first and second examples. In accordance with the increasedreceive impedance Z2, the transmit-band impedance (Tx1 to Tx2 in FIG.10A) of the receive filter is farther shifted to the higher impedanceside than that of the first and second examples. This makes it possibleto further enhance the transmit-and-receive isolation characteristics toa higher level than those of the first and second examples. The noisefigure can also be decreased to be smaller than that of the first andsecond example, and can be reduced to a minimal level.

FIG. 10B is a graph illustrating comparison results of the receive-bandtransmission characteristics between the duplexers and the low-noiseamplifiers according to the third example and the comparative example.This graph illustrates the transmission characteristics (DupRx-LNAtransmission characteristics) between the module common terminal 110 andthe module receive terminal 130. FIG. 10B shows that, when the receiveimpedance is about 110Ω, the transmission characteristics are lesslikely to deteriorate than in the comparative example in which thereceive impedance and the transmit impedance match the characteristicimpedance (about 50Ω). That is, as shown in FIGS. 10A and 10B, byreducing the gain of the transmit band in the receive path as a resultof separating the transmit-band impedance of the receive filter 10R evenfarther from the gain circles, the transmit-and-receive isolationcharacteristics can be improved while substantially maintaining thetransmission characteristics of the receive band.

In the transmit-and-receive module 1 including the low-noise amplifier30 having the above-described impedance characteristics, if the receiveimpedance is higher than about 110Ω (about 115Ω, for example), theinsertion loss and the noise figure in the receive band are increased.

When the transmit impedance is about 50Ω, the receive impedance can belower than about 115Ω. That is, the receive impedance can be higher thanthe transmit impedance by a factor smaller than about 2.3.

The present inventors have found that it is possible to enhance theisolation while decreasing the noise figure when the receive impedanceis higher than the transmit impedance by a factor smaller than about2.3, compared with when the receive impedance is equal to the transmitimpedance. The present inventors have also found that, when the centerpoint of NF circles of the low-noise amplifier is located on the higherimpedance side than that of gain circles is, if the output impedance inthe receive band of the receive filter 10R is set to be higher than theinput impedance in the transmit band of the transmit filter 10T by afactor of about 2.3 or greater, the gain of the low-noise amplifier issignificantly decreased and the noise figure thereof is also increased.When the receive impedance is higher than the transmit impedance by afactor smaller than about 2.3, the receiving noise figure can bedecreased substantially without necessarily decreasing the receivinggain.

Second Embodiment

In the first embodiment, a transmit-and-receive module for transmittingand receiving RF signals in a single frequency band has been discussed.In a second embodiment, a transmit-and-receive module for transmittingand receiving RF signals in multiple frequency bands will be discussed.

FIG. 11 is a circuit diagram of a communication device and atransmit-and-receive module 2 according to the second embodiment. Thecommunication device according to the second embodiment includes thetransmit-and-receive module 2 and a RF signal processing circuit 4. Thecommunication device may alternatively include the transmit-and-receivemodule 1 according to the first embodiment and the RF signal processingcircuit 4.

The RF signal processing circuit 4 performs signal processing, such asdown-conversion, on a RF received signal received from an antenna 3 viaa duplexer and a low-noise amplifier, and outputs the resulting receivedsignal to a baseband signal processing circuit (not shown) subsequent tothe RF signal processing circuit 4. The RF signal processing circuit 4also performs signal processing, such as up-conversion, on a transmitsignal received from the baseband signal processing circuit, and outputsthe resulting RF transmit signal to a power amplifier. An example of theRF signal processing circuit 4 is a RFIC.

The transmit-and-receive module 2 includes a switch 11, a high-bandtransmitter-and-receiver 2H, and a low-band transmitter-and-receiver 2L.

In the switch 11, a common terminal is connected to the antenna 3, afirst selection terminal is connected to the high-bandtransmitter-and-receiver 2H, and a second selection terminal isconnected to the low-band transmitter-and-receiver 2L. With thisconfiguration, the switch 11 connects the antenna 3 to the high-bandtransmitter-and-receiver 2H or the low-band transmitter-and-receiver 2L.Alternatively, the switch 11 may have a function of simultaneouslyconnecting the antenna 3 to the high-band transmitter-and-receiver 2Hand the low-band transmitter-and-receiver 2L.

The high-band transmitter-and-receiver 2H includes a duplexer 10H, apower amplifier (PA) 20H, a low-noise amplifier (LNA) 30H, a matchingcircuit 21H, an adjusting circuit 31H, a module transmit terminal 120H,and a module receive terminal 130H. The duplexer 10H includes a commonterminal 101H, a transmit terminal 102H, a receive terminal 103H, atransmit filter 10HT, and a receive filter 10HR. The transmit filter10HT is a transmit filter unit using a first transmit band as a passband and being connected to the common terminal 101H and the transmitterminal 102H. The receive filter 10HR is a receive filter unit using afirst receive band as a pass band and being connected to the commonterminal 101H and the receive terminal 103H.

The high-band transmitter-and-receiver 2H is the transmit-and-receivemodule 1 according to the first embodiment, for example.

To reduce the size of the high-band transmitter-and-receiver 2H, thepower amplifier 20H handling high-power signals and the low-noiseamplifier 30H handling low-power signals are integrated with each other.In a Smith chart, the output impedance of the receive filter 10HR is setso that the impedance in the receive band of the receive filter 10HRseen from the receive terminal 103H intersects a line connecting thecenter point of NF circles and that of gain circles.

The low-band transmitter-and-receiver 2L includes a duplexer 10L, apower amplifier (PA) 20L, a low-noise amplifier (LNA) 30L, a matchingcircuit 21L, an adjusting circuit 31L, a module transmit terminal 120L,and a module receive terminal 130L. The duplexer 10L is a secondduplexer including a common terminal 101L, (second common terminal), atransmit terminal 102L (second transmit terminal), a receive terminal103L (second receive terminal), a transmit filter 10LT, and a receivefilter 10LR.

The transmit filter 10LT is a second transmit filter unit using a secondtransmit band which is lower than the first transmit band as a pass bandand being connected to the common terminal 101L and the transmitterminal 102L. The receive filter 10LR is a second receive filter unitusing a second receive band which is lower than the first receive bandas a pass band and being connected to the common terminal 101L and thereceive terminal 103L.

The power amplifier 20L is a second power amplifier that amplifies a RFtransmit signal and outputs the amplified RF transmit signal to theduplexer 10L via the transmit terminal 102L.

The low-noise amplifier 30L is a second low-noise amplifier thatamplifies a RF received signal received from the antenna 3 via thereceive terminal 103L.

The low-band transmitter-and-receiver 2L is the transmit-and-receivemodule 1 according to the first embodiment, for example.

To reduce the size of the low-band transmitter-and-receiver 2L, thepower amplifier 20L handling high-power signals and the low-noiseamplifier 30L handling low-power signals are integrated with each other.In a Smith chart, the output impedance of the receive filter 10LR is setso that the impedance in the receive band of the receive filter 10LRseen from the receive terminal 103L intersects a line connecting thecenter point of NF circles and that of gain circles.

With the above-described configuration, in a multiband-support front-endcircuit, impedance matching between the duplexer 10H and the low-noiseamplifier 30H and between the duplexer 10L and the low-noise amplifier30L disposed in plural signal paths connected to the antenna 3 isperformed as follows. Instead of using the characteristic impedance,customized impedance reflecting the impedance characteristics of thelow-noise amplifier 30H is used for impedance matching between theduplexer 10H and the low-noise amplifier 30H, and customized impedancereflecting the impedance characteristics of the low-noise amplifier 30Lis used for impedance matching between the duplexer 10L and thelow-noise amplifier 30L. It is thus possible to provide atransmit-and-receive module which is small in size and which achievesthe optimized balance between the receiving noise figure and thereceiving gain according to the frequency band while plural duplexers,plural power amplifiers, and plural low-noise amplifiers supportingmultiple bands are integrated with each other, and to provide acommunication device including the transmit-and-receive module.

In the transmit-and-receive module 2 according to the second embodiment,at least one of the high-band transmitter-and-receiver 2H and thelow-band transmitter-and-receiver 2L may have the configuration and thefunction of the transmit-and-receive module 1 according to the firstembodiment. In the transmit-and-receive module 2, three or morefrequency bands may be used. That is, three or more signal paths, eachof which is constituted by a transmit signal path and a received signalpath, may be provided. In this case, at least one of the three or moretransmitters-and-receivers has the configuration and the function of thetransmit-and-receive module 1 according to the first embodiment.

Other Embodiments

The transmit-and-receive modules and the communication device accordingto embodiments of the disclosure have been discussed throughillustration of the first and second embodiments. However, certainelements in the above-described first and second embodiments may becombined to realize other embodiments, and various modificationsapparent to those skilled in the art may be made to the first and secondembodiments without necessarily departing from the scope and spirit ofthe disclosure. Such embodiments and modified examples are alsoencompassed within the present disclosure. Additionally, variousapparatuses integrating the transmit-and-receive module and thecommunication device described above therein are also encompassed withinthe present disclosure.

In the first and second embodiments, a transmit-and-receive module and acommunication device including a duplexer have been discussed by way ofexample. The present disclosure is also applicable to a quadplexer and ahexaplexer in which plural duplexers are connected to each other.

The configuration in which the output impedance (receive impedance) ofthe receive filter 10R is set to be higher than the characteristicimpedance and the input impedance (transmit impedance) of the transmitfilter 10T is not restricted to a particular configuration. For example,if the receive filter 10R is a surface acoustic wave filter includingresonators constituted by plural interdigital transducer (IDT)electrodes, electrode parameters such as the pitch of electrode fingersforming an IDT electrode, the interdigital width of the electrodefingers, the number of pairs of electrode fingers, and the distancebetween the reflector and the IDT electrode may vary among the IDTelectrodes. If the receive filter 10R is constituted by ladder elasticwave resonators, the impedance of the elastic wave resonator locatedclosest to the receive terminal 103 may be set to be higher than that ofthe other elastic wave resonators. With the above-describedconfigurations, high impedance can effectively be implemented whilemaintaining filter characteristics of the receive filter 10R.

Instead of setting the output impedance of the receive filter 10R to behigher, the impedance of the adjusting circuit 31 seen from thelow-noise amplifier 30 may be adjusted.

In the first embodiment, the receive band is a lower frequency side, andthe transmit band is a higher frequency side. However, atransmit-and-receive module according to an embodiment of the disclosuremay be applicable to a configuration in which the receive band is ahigher frequency side and the transmit band is a lower frequency side.

In a transmit-and-receive module according to an embodiment of thedisclosure, circuit elements, such as an inductor, a capacitor, and aresistor element, may be added between the module common terminal 110and the module transmit terminal 120 or the module receive terminal 130.

The present disclosure is widely applicable to communication terminals,such as cellular phones, as a high-gain, low-noise, smalltransmit-and-receive module and a communication device including such atransmit-and-receive module.

While preferred embodiments of the invention have been described above,it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the invention. The scope of the invention, therefore, isto be determined solely by the following claims.

What is claimed is:
 1. A transmit-and-receive module comprising: aduplexer comprising a common terminal, a transmit terminal, a receiveterminal, and a receive filter having a pass band that is a receiveband, wherein the duplexer is configured to receive a radio-frequencyreceive signal having a frequency in the receive band at the commonterminal and output the radio-frequency receive signal from the receiveterminal, and wherein the receive filter is connected between the commonterminal and the receive terminal; and a low-noise amplifier that isconnected to the receive terminal and that is configured to amplify theradio-frequency receive signal received from the receive terminal,wherein, as graphed on a Smith chart, an impedance in the receive bandof the receive filter as seen from the receive terminal intersects aline connecting a center point of noise figure circles and a centerpoint of gain circles, the center point of the noise figure circlesrepresenting the impedance at which a noise figure of the low-noiseamplifier is minimized and the center point of the gain circlesrepresenting the impedance at which gain of the low-noise amplifier ismaximized.
 2. The transmit-and-receive module according to claim 1, theduplexer further comprising a transmit filter connected between thetransmit terminal and the common terminal, wherein: as graphed on theSmith chart, an output impedance of the receive filter intersects theline connecting the center point of the noise figure circles and thecenter point of the gain circles; and an input impedance of the transmitfilter has a value that maximizes a gain of a power amplifier, whereinthe power amplifier amplifies a radio-frequency transmit signal andoutputs the amplified radio-frequency transmit signal to the transmitterminal.
 3. The transmit-and-receive module according to claim 1, theduplexer further comprising a transmit filter connected between thetransmit terminal and the common terminal, and the transmit-and-receivemodule further comprising: a power amplifier that amplifies aradio-frequency transmit signal and outputs the amplifiedradio-frequency transmit signal to the transmit terminal; a matchingcircuit that is connected between the transmit terminal and the poweramplifier, and that is configured to match impedance between thetransmit filter and the power amplifier; and an adjusting circuitconnected between the receive terminal and the low-noise amplifier andconfigured to adjust impedance between the receive filter and thelow-noise amplifier, wherein a value of receive impedance used forimpedance adjustment between the receive filter and the low-noiseamplifier is different from a value of transmit impedance used forimpedance matching between the transmit filter and the power amplifier.4. The transmit-and-receive module according to claim 3, wherein thevalue of the receive impedance used for impedance adjustment between thereceive filter and the low-noise amplifier is higher than the value ofthe transmit impedance used for impedance matching between the transmitfilter and the power amplifier.
 5. The transmit-and-receive moduleaccording to claim 3, wherein the value of the receive impedance is atleast 1.4 times greater than the value of the transmit impedance.
 6. Thetransmit-and-receive module according claim 3, wherein the value of thereceive impedance is less than or equal to 2.3 times greater than thevalue of the transmit impedance.
 7. The transmit-and-receive moduleaccording to claim 1, further comprising: a second duplexer comprising asecond common terminal, a second transmit terminal, a second receiveterminal, and a second receive filter having a pass band that is asecond receive band different from the receive band, wherein the secondduplexer is configured to receive a second radio-frequency receivesignal having a frequency in the second receive band at the secondcommon terminal and output the second radio-frequency receive signalfrom the second receive terminal; and a second low-noise amplifier thatamplifies the second radio-frequency receive signal received from thesecond receive terminal.
 8. The transmit-and-receive module according toclaim 7, further comprising an antenna terminal and a switch configuredto selectively connect either the common terminal or the second commonterminal to the antenna terminal.
 9. A communication device comprising:the transmit-and-receive module according to claim 1; and aradio-frequency signal processing circuit that receives theradio-frequency receive signal from the transmit-and-receive module, andthat processes the received radio-frequency receive signal.
 10. Thetransmit-and-receive module according to claim 2, further comprising:the power amplifier; a matching circuit that is connected between thetransmit terminal and the power amplifier, and that is configured tomatch impedance between the transmit filter and the power amplifier; andan adjusting circuit connected between the receive terminal and thelow-noise amplifier and configured to adjust impedance between thereceive filter and the low-noise amplifier, wherein a value of receiveimpedance used for impedance adjustment between the receive filter andthe low-noise amplifier is different from a value of transmit impedanceused for impedance matching between the transmit filter and the poweramplifier.
 11. The transmit-and-receive module according to claim 4,wherein the value of the receive impedance is at least 1.4 times greaterthan the value of the transmit impedance.
 12. The transmit-and-receivemodule according to claim 10, wherein the value of the receive impedanceis at least 1.4 times greater than the value of the transmit impedance.13. The transmit-and-receive module according claim 4, wherein the valueof the receive impedance is less than or equal to 2.3 times greater thanthe value of the transmit impedance.
 14. The transmit-and-receive moduleaccording claim 10, wherein the value of the receive impedance is lessthan or equal to 2.3 times great than the value of the transmitimpedance.
 15. A communication device comprising: thetransmit-and-receive module according to claim 2; and a radio-frequencysignal processing circuit that receives the radio-frequency receivesignal from the transmit-and-receive module, that processes the receivedradio-frequency receive signal, that processes the radio-frequencytransmit signal, and that outputs the radio-frequency transmit signal tothe power amplifier.
 16. A communication device comprising: thetransmit-and-receive module according to claim 3; and a radio-frequencysignal processing circuit that receives the radio-frequency receivesignal from the transmit-and-receive module, that processes the receivedradio-frequency receive signal, that processes the radio-frequencytransmit signal, and that outputs the radio-frequency transmit signal tothe power amplifier.